#include <fstream>
#include <deque>
#define N 5000010
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long long sol;
int n,i,x[N],k;
deque <int> q;
int main()
{
    fin>>n>>k;
    for(i=1;i<k;i++)
    {
        fin>>x[i];
        while(q.size()&&x[i]<=x[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    for(i=k;i<=n;i++)
    {
        fin>>x[i];
        while(q.size()&&x[i]<=x[q.back()])
            q.pop_back();
        q.push_back(i);
        if(q.front()==i-k)
            q.pop_front();
        sol+=x[q.front()];
    }
    fout<<sol;
    return 0;
}